My Pro master machine has the same linnear tension clamp. The 2 center plates pull together as tension is pulled. It appies the proper pressure against the string as needed as the clamps will close completely together if no string, therefore I do not believe there is an adjustment as it automatically applies the proper pressure to hold the string, as the 2 center plates will move foward and as it does that it closes together. If it is slipping, then I believe that it needs to be thoroughly cleaned.You may also check to see that the 2 center plates do move freely towards the front, and close together all the way, as that could be binding. You should be able to move those plates easily foward, and they should spring back quickly to the resting position by itself easily as well. I would take the tension plated apart by dissembling them and clean them properly. I always kept mine clean, and so far I have not yet needed to dissemble it, but they always held without slipping to date.I have always cleaned them after 20 or so racquets.I guess preventative maintainance helps.

(Also from looking at your pictures, the 2nd picture the plates do not look evenly parallel, where mine are, maybe it is just the camera angle, but mine are perfectly parallel, yours look narrower towards the front, maybe something in there binding it?)